10KVA inverter Design Project

[schmitt trigger]

The lowest you should discharge each individual cell safely is 1.75V, thus for 48 cells the cutoff voltage should be 84 V.

It can be done with a voltage divider feeding the noninverting input of a comparator. The inverting input goes to a reference like the ubiquitous TL431....the comparator output will swing low at the cutoff voltage.
Further improvements can be to add a couple seconds delay after the comparator output, to allow momentary voltage dips without triggering the alarm.

 

[Ogu Reginald]

Do not forget that most ICs can not work above 18V but here what we are monitoring is 84V. So how can i step down the voltage? I can easily get a reference voltage, Sometimes the voltage divider like you mentioned may pass 18V. Wouldn't this destroy the comparator?

 

[schmitt trigger]

Assuming a reference voltage of 2.5V (TL431), you can use a voltage divider consisting of a 2.5k (on the bottom) and a 81.5k (on the top). Nearest standard resistor values are (2.4k+ 100) and (82k in parallel 10Meg).

 

[Ogu Reginald]

I have tried it and it is working thank you.

 

[Paul Dent]

Everything you have been told so far is BS I am afraid.

I presume you are wanting to make 120v 60Hz or 240v 50Hz for household current?

Then you have to decide what waveform you need. There are three choices:

Square Wave, Modified Square Wave or Sine Wave.

A square-wave of +/- 120 volts has the same power as a 120v rms house current
but has only 70% of the peak value. Therefore appliances that use peak rectification
might complain about that.

The modified sine wave goes up to +1.414 x desired rms value for T/4, zero for T/4,
down to -1.414 x rms for T/4, back to zero for T/4 then repeats. This has the same
rms and peak value as household current. This is much better also for the output transformer,
which needs periods at zero to balance the flux (center taps are never perfect).
In inverter design, this is called "notching".

However, there are appliances that derive internal voltages by using capacitive voltage
droppers that will not work with this, as they assume a sinewave spectrum.
I have seen this in dryers, microwaves. electric and gas ovens and cellphone and laptop chargers.

The only thing sure to work with all appliances is a sinewave inverter, and these are more
complicated to make efficient. The best design I know that has been around for a while is the TRACE/XANTREX SW4048
which generates 4.5KVA , 120v 60HZ from 48V DC

There are many other issues with high power inverters.

1. Do you want to power loads that have a non-unity power factor, like motors, HVAC, fluoeresecent lights etc?
If so, you need a design that allows power flow in the reverse direction for part of the cycle.
Only MOSFETs will do this reliably.

2. A big issue is protection against overcurrent, overvoltage, overtemperature, ground faults, inrush current etc
If you are using 8 car batteries in series to get 96 volts, if you get a bad fault, there will be smoke and flames
everywhere. You will need fuses or preferably a DC-rated circuit breaker. Some AC circuit breakers will work if
their AC voltage rating is about 5 times your DC voltage. So a 600V AC breaker should be good for 96V DC.

By the way: do not put capacitors across the output of a squarewave inverter. You will burn it out for sure.
A low pass filter to get rid of the huge radio interference caused by such a beast needs to have series inductors first.
I use 10uH 55 amp inductors that are pretty huge, followed by shunt 1uF capacitors. That's on a 7KVA inverter. There is a safe filter circuit and a dangerous filter circuit. The dangerous filter circuit is the one commonly used on all electronic equipemnt including PCs, and I have seen people shocked and equipment damaged by it. It has the characterstics that if you lose the ground, the equipemnt case will rise to half the supply voltage. Not nice if you are about to transfer wet clothes from the washer to the dryer and the dryer case is at 120 volts AC. A safe filter circuit does not connect capacitors from the hot leg to ground/case.

 

[Ogu Reginald]

I have looked at your suggestion but I don't understand what you mean by BS.

 

[FvM]

Another word for cow dung. :smile:

 

[Ogu Reginald]

The inverter has been working well. It have served for lighting pruposes, it has powered 9kVA lighting load continously. But I disconnected all the lighting load leaving only one 200 watt bulb and as soon as I connected an ordinary 120 watt fan, the bank of MOSFET was completely burnt.
1.Please can someone tell me the problem and solution.
2. Is it normal for transformers to hum?

 

[pradeep.g.belchada]

transformer will produce noise. but for your 10kva inverter how much dc link voltage u selected

 

[Ogu Reginald]

What do you mean bny DC links? I don't understand you.

 

[pradeep.g.belchada]

i mean how much total battery voltage utilised

 

[FvM]

i mean how much total battery voltage utilised

It has been all reported during this thread.

 

[23mughalcenter]

10 kva inverter

i have design that works 500va to 20000va and very simple sine wave but i need dollars if you pay me i will help you

 

[pradeep.g.belchada]

i have design that works 500va to 20000va and very simple sine wave but i need dollars if you pay me i will help you

i have desgin that works from 500va to 5kva i will give it free

 

[Ogu Reginald]

Please my brother in as much as my inverter is working, can you upload the details (circuit diagram) of your design le me modify my own.

Please this site is not for merchants.